A variable directivity antenna is used to selectively receive radio waves coming from different directions. An example of such variable directivity antennas is disclosed in Japanese Utility Model Publication No. SHO 63-38574 (Y2) published on Oct. 12, 1988, assigned to the same assignee of the present application.
According to the technique disclosed in this UM publication, first and second antennas are disposed at right angles to each other in the same horizontal plane. The first and second antennas may be dipole antennas or folded-dipole antennas. A signal received by the first antenna is coupled through a first variable attenuator to a combiner, to which a signal received by the second antenna is also coupled through a second variable attenuator. The amounts of attenuation provided by the first and second variable attenuators are varied to change the directivity of the variable directivity antenna.
Because the directivity can be rotated, the variable directivity antenna of the Japanese UM publication can select and receive only a desired one of radio waves coming to the antenna from various directions. This antenna, however, has an 8-shaped directivity pattern, it also receives a radio wave coming to it from the direction opposite to the direction of the desired radio wave, and, therefore, its F/B ratio is low.
Therefore, an object of the present invention is to provide a small-sized antenna apparatus with an improved F/B ratio, which can selectively and satisfactorily receive radio waves coming to the antenna apparatus from different, two directions. Another object of the present invention is to provide a receiver system with a variable directivity antenna apparatus which can selectively and satisfactorily receive radio waves coming to the antenna from various directions.